Thermosensitive recording material may be coated or impregnated with a thermochromic compound capable of developing color upon exposure to heat. The thermosensitive material may be fed through a thermal printer to selectively heat the thermochromic compound, which may change color in the heated locations to produce a visible image. Such images may be produced in one or two colors, where development of a second color may occur by subjecting one thermochromic compound to two levels of heat. Low heat may develop a first color and high heat may bleach the first color and develop a second color.
Such thermosensitive recording materials may have the drawback of being relatively non-permanent and sensitive to environmental conditions such as heat, light and/or moisture. Overexposure to those and other conditions may lead to a fading or darkening of the visible image and/or paper background, thereby reducing the legibility of the visible image. This may present relatively serious problems, as in the case of a pharmaceutical label, where important prescription information may be compromised. Furthermore, overexposure to degrading influences may directly jeopardize the safety and/or efficacy of the products (e.g. pharmaceuticals) which thermosensitive labels typically serve to identify.